The posterior distribution of time t
and rate r
for a dataset of two sequences with 100 sites and 55 differences. Gamma priors are used for time and rate, while sequence distance is calculated under the Jukes-Cantor model. With more and more sequence data, the posterior of time and rate will converge to a curve (instead of a point). Because the sequence data provide information about distance only, posterior estimates of time and rate will have uncertainties even with an infinite amount of sequence data. The situation is the same when we date species divergences using uncertain fossil calibrations. See figure 3c in DOS REIS & YANG, pp. 30–43 in this issue.